For some years, modern forestry has been developing towards an increasingly higher degree of mechanisation. For working duties where chain saws were previously used, “two stage grip” forestry machines began to be employed in the 1970s, which entailed that the manual handling of trees and timber declined. Such forestry machines are characterised by having a gripping device which grasps the tree to be felled already in connection with the felling operation. Thereafter, the tree is grasped once more and moved to a trimming unit, preferably on the same forestry machine. This treatment thus takes place in two stages, and in daily parlance this type of machine is therefore known as a “two stage gripper”.
During the 1990s, the forestry machines were even further refined and made more efficient, and forestry machines which grasp the tree to be felled, carry out the felling operation, and also trim and cut the tree in one and the same operation were introduced. This type of forestry machine is called in daily parlance a “single stage gripper”, since the tree is grasped only once. This younger generation of forestry machines is not only more rapid and more efficient but also lighter. The earlier “two stage grippers” had a weight of between 20 and 30 tonnes, while the new machines weigh only 15 to 20 tonnes. Both types of machines run on inflatable rubber wheels which have a large springing ability.
Since the tree which is cut and handled has a considerable mass, this results in pronounced swaying and jolts in the forestry machine when the tree bends or is moved at all by the machine. In addition to these movements, there are also movements which are the result of the uneven terrain, and also vibrations from engines, hydraulic systems, fans, pumps and the like. Taken as a whole, these movements result in an extremely unpleasant and unsuitable working environment for the operator controlling the machine.
The operators are afflicted by numerous problems as a result of the constant turnings and movements of the forestry machine, for example nausea, headaches, fatigue and loss of concentration. Since the operators must constantly parry these often random movements, problems also occur in muscular tension. In the long term, the poor working environment has resulted in wear and tear on the operators, in the skeleton, joints and muscles, and the risk of sickness absenteeism and early retirement is high.
The movements of the forestry machines are even so pronounced that the operators fend off to parry such movements and at worst to such a degree that the operating devices are subjected to extreme stresses and run the risk of being snapped off. While safety belts are mounted in most forestry machines, they are experienced by the operators as impractical and inconvenient and, as a result, are seldom worn.
In certain-cases, downright dangerous situations may occur such as in the cutting of wind-felled trees. Such trees are occasionally trapped under other trees and can powerfully spring back on being cut and cause serious personal injury as well as damage to equipment.
In addition to the human suffering, there are also economic aspects to this problem. When the operators are afflicted by the above-mentioned problems, their productivity is reduced, among other things because of difficulties in concentrating and fatigue. The need for breaks increases far beyond that which is normal for the average in working life. The risk of faulty judgement and negligence also increases, which may involve additional costs for scrapped machinery. Even more serious is that such faulty judgement and negligence may lead to injury to human beings and also to costly repairs to equipment. Reduced productivity may even take such expression that operators are disinclined to move themselves and their forestry machines more than is necessary, with the result that, among other things, felled trees lie scattered about in the terrain and efficient transport is impeded. Moreover, the transport vehicles increase the wear stresses on the land.
The above-outlined problems have increased because of a growingly unfavourable relationship between the mass of the felled tree trunks and the mass of the machine. At the same time as the machines have become lighter and quicker, development has also moved towards higher awareness in matters relating to the working environment and, in addition, there are now stricter demands on comfort than before.
One conceivable attempt to solve this problem could be to provide the forestry machine with collapsible stabiliser feet, but, on the one hand, the protraction and retraction of such feet takes far too long a time and, on the other hand, the terrain is seldom flat enough and firm enough for such feet to be usable.
A further problem inherent in existing forestry machines is visibility. Granted, the cab of the operator is in an elevated position and an overview of the units of the machine is quite good, but one result of the elevated placing of the cab is that it is difficult to see the surrounding terrain, and objects which are located in the vicinity immediately close to the forestry machine. Another problem concerning visibility is that the terrain and surrounding trees constitute restrictions in the choice of the position of the forestry machine. This may entail that the operator is forced to work looking into the sunlight, which partly affects safety and partly increases fatigue and the discomfort as described above.
The noise level in forestry machines is generally quite high and fatiguing in the long term. Moreover, this affects concentration, with resultant problems, and also increases the risk of damage to hearing. Granted, some form of hearing protection can be employed, but they are seldom used in practice, since they are experienced by the operator as an obstacle to his work.
In order to reduce turning movements, jolts and vibrations, various types of suspension devices for the operator's driving seat have been worked on. A few examples of devices employed are hydraulic dampers, friction dampers and compensation with the aid of electronic transducers. Unfortunately, the results have not come up to expectation, partly because the damping does not function adequately, and partly because, even if the seat is kept relatively still, the surrounding cab will move, which entails that problems in travel sickness, fatigue and difficulties in concentrating will be more or less the same as before.
Another attempted solution is to apply the same type of damping and suspension to the cab as a whole, but, on the one hand the damping is insufficient, and, on the other hand, the rest of the machine will continue to move, for which reason the above-outlined problems of travel sickness and fatigue remain unsolved.
Hence, the above problems together combine to form an extremely unsuitable working environment and attempts have been made to come to grips with at least a part of these problems. However, at worst the solutions may counteract each other. An elevated cab which, to some degree improves visibility, has the disadvantage that it entails even more pronounced pivotal movements for the operator when the forestry machine is driven in certain types of terrain.
As was mentioned above, safety belts to restrain the operator and reduce muscular tension are seldom used since they are experienced as being impractical and inconvenient.